1. Field of the Invention
The invention relates to a lens, and more particularly to a zoom lens.
2. Description of the Related Art
A consumer digital still camera is almost equipped with a zoom lens, the zoom ratio of which has been developed from 2, 3, and 5 times in early stages, through 10 and 12 times, to more than 20 times recently. A zoom lens differs from a fixed focal length lens in that the focal length of a zoom lens is adjustable within a certain range. When a zoom lens zooms to a telephoto end, the distant object looks closer and magnified. When a zoom lens zooms to a wide-angle end, the field of view is expanded to accommodate a wider range of image. The fixed focal length lens doesn't have zoom in and zoom out function as the zoom lens has.
The zoom lens is developed toward high zoom ratio as a variety of applications are required by users. Furthermore, the requirement of image quality is also rising. However, it is not easy to achieve that a zoom lens of a high zoom ratio has a good optical performance.